The present invention relates to a method for the electroless deposition of nickel coatings on surfaces of metals and metal alloys and to an aqueous depositing bath therefor containing a nickel compound, complex salts, sodium hypophosphite, and copper salt.
The electroless deposition of nickel is a well-known and frequently used process. Electroless deposition processes and baths therefor and known, as evidenced, for example, in Britsh Pat. Nos. 1,378,458; 1,448,831 and 1,507,965. The baths described in these patents are suitable for electroless nickel plating of steel, non-ferrous metals, aluminum, plastics and ceramics. However, it was not possible to obtain faultless nickel coatings having good corrosion protection using these baths for the coating of magnesium or magnesium alloys.
Resort to further measures heretofore employed for corrosion protection of magnesium and magnesium alloys (MgAl6Zn and GD-MgAl9Znl) was successful. Chromatizing according to the BAS-process and black chromatizing yielded somewhat improved, yet still unsatisfactory, corrosion protection for magnesium and magnesium alloys; moreover, such coatings display low abrasion resistance.